The purpose of this study is to identify predictors of mental retardation in a population of 37,000 children followed from the prenatal period to age 7. The incidence of mild retardation (1% in whites and 5% in blacks) and to a lesser degree, of severe retardation (0.5%) was inversely related to socioeconomic status. Among the severely retarded, 25% of whites and 50% of blacks had no major genetic or neurological abnormality. Perinatal risk factors for the severely retarded group as a whole include Down's syndrome, major CNS malformations, neonatal seizures and clinical signs of perinatal hypoxia. For the subgroup of severely retarded with unknown etiology, perinatal risk factors include non-CNS malformations, peripheral nerve abnormalities, signs of hypoxia, and maternal urinary tract infection during pregnancy. A report on teenage pregnancy as a risk factor for poor cognitive outcome has been published. This study is completed and a monograph is in preparation.